1. Technical Field
The subject matter described herein relates to a type of retroreflective pavement marking tape with spread-out features designed to improve retroreflectivity and decrease cost.
2. Description of the Related Art
The idea of marking pavement using retroreflective tapes (whether durable/permanent or removable) has a long history, dating back to at least the mid-1970s when multilayered, retroreflective laminate materials intended to be used for road and highway marking, among other applications, were developed. Although they may have incorporated some crowning (i.e., thicker in the middle than along the edges), these tapes were generally flat. However, in the early 1990s a series of pavement marking tapes were developed that had raised, regularly spaced, square-shaped embossed features intended to improve retroreflectivity by placing the reflective elements (generally, microscopic glass beads) on the vertical faces of the raised square bosses or bumps, rather than on a uniform horizontal surface. Generally speaking, this tactic is extremely effective, although such tapes are somewhat more difficult to manufacture.
The raised features also improve drainage during rain, and delay the moment when the tape is completely covered under conditions of snow or minor flooding. Furthermore, because the retroreflective elements are on the vertical rather than the horizontal faces, they are somewhat better protected from mechanical abuse due to tire hits and snow plows. However, these are not thought to be primary motivations for the development of these embossed tapes.
During the 1990s it was noticed that with this plurality of regularly spaced and closely packed features, there is a shadowing or interference effect wherein each raised bump blocks the view of the ones behind it. Thus, for any given viewing angle some bumps are “wasted” in the sense that they do not contribute to overall reflectivity, and can even detract from it. New relief patterns were therefore developed in which the raised squares were more widely distributed and also less regularly distributed, and covered between 15% and 45% of the total surface. This change reduces the shadowing effect, improving retroreflectivity while simultaneously requiring less material (rubber matrix, pigment, polymer topcoat, glass beads, etc.) to manufacture. Such tapes represent the current state of the art.
The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded as subject matter by which the scope of the claimed invention is to be bound.